Oxybisphthalimides, for example, 4,4'-oxybis-(N-methylphthalimide), are readily converted by hydrolysis to oxydiphthalic anhydrides, in particular 4,4'-oxydiphthalic anhydride, which is a well known monomer useful in the synthesis of polyimides having good thermal and solvent resistance properties.
The preparation of 4,4'-oxybis-(N-methylphthalimide) (OBI) by heating a solution of 4-nitro-N-methyl-phthalimide (NPI) with potassium fluoride, potassium or sodium nitrite in a dipolar aprotic solvent, e.g., DMF, Me.sub.2 SO or NMP and the like, at elevated temperatures has been reported by Markezich, et al., "Reactions of Fluoride and Nitrite Ions with 4-nitrophthalimides", Journal of Organic Chemistry 42, 3481 (1977). OBI has also been synthesized by refluxing NPI with potassium acetate in DMF. The preparation of OBI BY HEATING NPI in a dipolar aprotic solvent in the presence of alkali metal carboxylates has also been reported in U.S. Pat. No. 4,780,544.
The use of dipolar aprotic solvents, e.g., DMF, NMP, sulfolane, DMAc and DMSO, in such methods as described above, however, is undesirable in that such solvents are typically expensive, hard to process and difficult to recycle. A need therefore exists for a process of preparing oxybisphthalimides which utilizes less expensive, relatively nonpolar solvents, which are easier to process and recycle.